If God is so good, how can he allow such evil to exist in the world? This easily one of the most popular atheistic arguments, next to The Omnipotence Paradox and The Omniscience/Free Will Paradox. For a few thousand years, it was a solid argument against the biblical God, but has now been resolved.
The Problem of Evil
The original Problem of Evil is often attributed to an ancient Greek philosopher named Epicurus, who lived from 341-270 BC. It first went like this:
If an all-powerful and perfectly good god exists, then evil does not.
There is evil in the world.
Therefore, an all-powerful and perfectly good god does not exist.
This argument claims that the existence of evil in the world is not consistent with the characteristics of an all-powerful, all-knowing, all-good God. This argument was eventually refined into the following:
God is omnipotent, omniscient, and perfectly good.
A perfectly good being would want to prevent all evils.
An omniscient being knows every way in which evils can come into existence.
An omnipotent being, who knows every way in which an evil can come into existence, has the power to prevent that evil from coming into existence.
A being who knows every way in which an evil can come into existence, who is able to prevent that evil from coming into existence, and who wants to do so, would prevent the existence of that evil.
If there exists an omnipotent, omniscient, and perfectly good being, then no evil exists.
Evil exists (logical contradiction).
The argument then says that a God who claims omnipotence, omniscience, and omnibenevolence cannot exist if there also exists evil in the world. The biblical God claims these three attributes, and there also exists evil in the world, so the biblical God cannot exist.
After all, if God was omnipotent, and omniscient, then he must not be omnibenevolent, because he knows evil is there, and has the power to stop it, but does not apparently will it.
If he is omnipotent and omnibenevolent, then he must not be omniscient, because he has the power to stop it, and wills that it should be stopped, but does not apparently know it is there.
If he is omnibenevolent and omniscient, then he must not be omnipotent, because he knows evil is there, and wills that it should be stopped, but apparently has not the power to stop it.
The problem of evil went unanswered for about 2000 years, but now, philosophers and theologians mainly consider it sufficiently refuted by Plantinga's free will defense.
Evil and Free Will
It is commonly admitted among theologians and philosophers that God's power does not extend to logical contradictions. For example, he cannot create a four-sided triangle or a married bachelor. It's a contradiction of terms. By the same logic, he cannot force an agent to freely choose good.
Therefore, Plantinga argues that it is impossible for God, even being omnipotent, to create a world of free creatures in which there is no evil. Plantinga summarizes his argument:
“A world containing creatures who are significantly free (and freely perform more good than evil actions) is more valuable, all else being equal, than a world containing no free creatures at all. Now God can create free creatures, but He can't cause or determine them to do only what is right. For if He does so, then they aren't significantly free after all; they do not do what is right freely. To create creatures capable of moral good, therefore, He must create creatures capable of moral evil; and He can't give these creatures the freedom to perform evil and at the same time prevent them from doing so. As it turned out, sadly enough, some of the free creatures God created went wrong in the exercise of their freedom; this is the source of moral evil. The fact that free creatures sometimes go wrong, however, counts neither against God's omnipotence nor against His goodness; for He could have forestalled the occurrence of moral evil only by removing the possibility of moral good.”
It is impossible to create a world in which the creatures are free to be morally good and morally evil, and yet they cannot choose evil. It is equivalent to say that the creatures both are, and are not, free. It is just as impossible as creating a four-sided triangle or a married bachelor. It would be like bringing the agent to a fork in the road and telling him he may travel either way, yet one path is clearly blocked. Granting the freedom to travel either path would then be meaningless.
So not only are the attributes of the Christian God (omnipotence, omniscience, and omnibenevolence) not logically inconsistent with the presence of evil in the world, but rather it seems that it is absolutely necessary in order to achieve any good.